The present invention relates to a method of producing filter floors for treating water and more specifically draining filter floors with suction strainers or nozzles, supporting the filtration material.
It is known that certain filtration operations in the domain of water treatment are performed through filters, particularly filters with a granular filtration material, whose structure, generally made of reinforced concrete, mainly comprises a liner comprising a raft which rests on peripheral walls, and a perforated floor supporting the filtration material.
The functions of such floors are well known to the specialist. These are, in addition to supporting the filtration material, to allow the liquid, particularly the water filtered by the said material during the filtration phase, to pass through and to flow, and to allow for the passage and distribution of fluids during the washing phase.
In general, these filter floors comprise a structure made up of girders or columns, which supports a monolithic slab or a collection of prefabricated slabs.
As far as producing the floor support structure is concerned, there are various possible solutions, specifically:
casting concrete girders or columns in the filter liners;
laying prefabricated girders or columns in the filter liners.
There are also various techniques for producing the upper part of the floor.
Thus, FR-A-2,596,385 reveals a method which consists in assembling prefabricated small-sized slabs or sheet which are installed, connected and fixed to the girders or columns of the support structure by an appropriate anchoring system.
EP-A-0,324,673 describes a method which consists in casting a reinforced concrete slab on lost formwork previously installed on the girders or columns that constitute the filter floor support structure.
There are also techniques involving casting the concrete of the entire support structure/monolithic slab in a single phase, but this technique entails the use of several types of lost formwork for producing the girders or columns and the slab, respectively.
These known techniques exhibit a certain number of drawbacks. Specifically, they entail:
either the assembling of numerous prefabricated elements (slabs, rods, bolts, seals, etc) which is tricky, lengthy and expensive to implement;
or the use of girders, then pre-slabs or lost formwork placed on the girders and finally the casting of a concrete slab, the overall implementation of which proves tricky and expensive;
or the assembly of several types of lost formwork to produce the support structure/slab assembly, this technique also being characterized by being tricky and expensive to implement.
To alleviate the drawbacks of the previous techniques mentioned above, the present invention proposes to provide a method of producing a concrete filter floor which makes it possible to reduce the implementation times and therefore the cost prices.
In consequence, the subject of this invention is a method of producing a filter floor for treating water, comprising a structure made of girders or columns supporting a slab which has a number of orifices intended to take suction strainers, characterized in that the concrete of the said structure and of the slab is cast directly into the filter liner, the said structure and the lower part of the slab being shaped by one single design of lost formwork.
The method according to the invention comprises the following successive steps:
producing the filter liner,
installing the reinforcement for the girders or columns of the filter support structure;
positioning lost formwork and securing it;
mounting rings, protected by caps, on the lost formwork at the locations intended for the suction strainers;
producing the reinforcement of the upper part of the slab;
casting the concrete of the support structure and of the slab,
removing the caps that protect the rings and mounting suction strainers (11) on the said rings.
According to the invention, the support structure and the slab may be cast in a single stage or in two stages.
The invention is also aimed at lost formwork for implementing the method as defined hereinabove and as a filter for treating water, comprising a concrete floor laid in accordance with this method and employing lost formwork as specified hereinabove.